. Fresh-water biology. Freshwater biology. THE FRESH-WATER ALGAE 175 Only one genus listed here. Plant upright, many centimeters long, differ- entiated into a pseudo-parenchymatous principal axis and branches, covered with short, unbranched hairs. Color an olive brown Thorea Bory. Reproduction asexual only, con- sisting in the formation of sporangia on the outer surface of the axis, each containing but a single spore, without cilia and without membrane. The position of this alga in the sys- tem of classification is very doubtful, but for convenience it is placed with the Phaeophyceae. Fig. 248
. Fresh-water biology. Freshwater biology. THE FRESH-WATER ALGAE 175 Only one genus listed here. Plant upright, many centimeters long, differ- entiated into a pseudo-parenchymatous principal axis and branches, covered with short, unbranched hairs. Color an olive brown Thorea Bory. Reproduction asexual only, con- sisting in the formation of sporangia on the outer surface of the axis, each containing but a single spore, without cilia and without membrane. The position of this alga in the sys- tem of classification is very doubtful, but for convenience it is placed with the Phaeophyceae. Fig. 248. Thorea ramosissima Bory. Portion of a longitudinal radial section. X about ISO. (After Hedgecock & Hunter.). Class IV. Rhodophyceae Color red, or a dull, purplish green; plant sometimes complex in structure; reproduction sexual and in most cases asexual also. Only one order Florideae. Plants mostly inhabitants of salt water, but represented in fresh water by several genera. The structure of the different fresh-water genera varies, but the sexual form of reproduction is essentially the same in all. The male reproductive organs are borne on the ends of filamentous branches, the contents of each of which produce a single spermatium. The female organ is flask-shaped, in the larger portion of which, the carpogonium, Hes the oosphere; through the long neck, the trichogyne, the spermatium is conducted to the oosphere at the base, it having been previously carried by the water to the projecting tip of the trichogyne. As a result of fertilization, densely branched filaments arise from the base of the carpogonium, on the ends of which are borne carpospores; these spore-bearing branches, and the sterile branches which usually surround them, together form the cystocarp. In Chanlransia and in many salt- water species tetraspores are also formed. 1 (8) Plant branched 2 2 (s) Branches simple and not in whorls 3 3 (4) Plants coarse, of simple or occasionally branched, hollow, tapering br
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectfreshwa, bookyear1918
